*INTRODUCTION

Stanford Type B aortic dissections (TBAD) involve an entry tear in the intima of the thoracic aorta, distal to the left subclavian artery, and allow for false lumen (FL) development and expansion over time.1 Most often, the true lumen supplies the celiac axis, superior mesenteric artery, and right renal artery, while the false lumen supplies the left renal artery.2 False lumen expansion and distal extent of the dissection can progress to arterial compromise in the visceral segment and lower extremities, leading to end-organ malperfusion and ischemic events.

Medical management is the mainstay for uncomplicated TBAD, but those with high-risk anatomic features, refractory pain, or uncontrolled hypertension may benefit from TEVAR.3 The objective of a TEVAR is to occlude the entry tear and promote false lumen thrombosis, which would help depressurize the aorta and minimize the risk of aortic degeneration.4 In this study, we aim to present short- and long-term outcomes of TEVAR for acute, subacute, and chronic TBAD at a tertiary referral center, emphasizing lesion characteristics, utilizing Vascular Quality Initiative (VQI) cases.

METHODS

Selection of Patients and Procedure Details

All patients (n = 173) who underwent TEVAR at Stony Brook University Hospital between 2010 and 2022 were identified using the local Vascular Quality Initiative registry. Patients who had acute, subacute, or chronic TBAD were included. Those with residual TBAD after type A repair was excluded. Patients undergoing hybrid thoracoabdominal procedures (combining endovascular techniques with open debranching or bypass) were excluded. After inclusion and exclusion criteria were applied, the number of patients studied in our cohort was thirty-three.

Patients were classified by the timing of TEVAR from the onset of symptoms: hyperacute (0-2 weeks), acute (2-12 weeks), subacute or chronic (> 12 weeks), and asymptomatic versus symptomatic status. Indications for treatment in subacute or chronic TBAD cohort included refractory chest, abdominal, or back pain or uncontrolled hypertension. TEVAR case planning was performed using three-dimensional reconstruction software, and the case was discussed preoperatively at case conferences among multiple vascular surgeons. Spinal drainage was performed at the surgeon’s discretion based on anticipated aortic length coverage or concern for spinal cord ischemia postoperatively. Anti-thrombotic therapy with anti-platelets (e.g., aspirin, clopidogrel) or anti-coagulants was administered pre- and post-procedurally based on the operator’s preference. Follow-up consisted of in-person visits with CT angiography at 48 hours postoperatively, 1 month, 6 months, 12 months, and annually thereafter, unless an endoleak was detected, in which case closer surveillance was undertaken at the discretion of the operator.

Data Collection

Patient characteristics and preoperative comorbidities were collected from the electronic medical record, including a history of hypertension (HTN), coronary artery disease (CAD), and prior aortic surgery (Table 1). Operative details and adjunct procedures were registered. Important lesion characteristics, including thoracic and abdominal aorta diameters, number of re-entry tears, and determination of luminal flow to visceral arteries, were measured using Computed Tomography Angiography (CTA) and registered (Table 2). The measurements were performed on CTA images with intravenous contrast in the arterial phase, with the absence of contrast in the false lumen suggestive of false lumen thrombosis.

Study Outcomes

The primary outcomes of our study included all-cause mortality, any endoleak, and any aortic reintervention related to the index TBAD repair. Secondary outcomes included the rate of major complications perioperatively (i.e., within 30 days) and during follow-up (i.e., rupture, retrograde type A dissection, immediate type IA endoleak, and ESRD). Maximum diameter in the thoracic and abdominal aorta was also measured during follow-up to assess for aortic remodeling.

Statistical Analysis

Categorical variables were presented as absolute and relative frequencies (i.e., percentages), while continuous variables were presented as means ± standard deviations. The cumulative incidence of primary and secondary outcomes was also presented with absolute and relative frequencies. Furthermore, the Kaplan-Meier (KM) method was used to estimate the 24-month freedom from primary and secondary endpoints. All analyses were performed using STATA software (version 14.1; STATA Corporation, College Station, TX, USA).

RESULTS

Patients and lesion characteristics

The average age of this patient cohort was 63.0 ± 13.6 years. Most of the patients were Caucasian males and had a history of hypertension. About one-fourth of the patients had diabetes and coronary artery disease (CAD) at presentation. Most of the cases were symptomatic (78.8%) and were treated in the hyperacute (54.6%) or acute setting (24.2%). Involvement of the thoracoabdominal aorta with dissection extending to the common iliac arteries was observed in 54.6% of the cases, with the false thoracic lumen being completely patent in most cases. The average maximum thoracic and abdominal aortic diameters were 37.9 ± 12.3 mm and 29.9 ± 11.9 mm, respectively. Details regarding patients’ baseline demographics and lesion characteristics are summarized in Tables 1 & 2, respectively.

Procedural characteristics and short-term outcomes

As this was a retrospective study, all included patients were deemed suitable candidates for TEVAR, and no patients were denied treatment for anatomical reasons. Stent grafts were deployed in all cases, followed by bare metal stents in 12.1%. The average initial covered length of the aorta was 166 ± 36.9mm. Intravascular ultrasound (IVUS) was used in 81.8% of the cases, and transesophageal echocardiography (TEE) was utilized in 9.1% of the cases to facilitate accurate deployment. The stent grafts were placed at zone 2 in 48.5% of the cases. Left carotid subclavian bypass was performed in 9.1% during the same admission, while 3% of the cases underwent left subclavian snorkeling stenting during the same procedure. A spinal drain was placed in 51.5% of the cases. Details are presented in Supplementary Table 1.

The average procedure time was 175 ± 117.5 min, with an average fluoroscopy time of 28.9 ± 27.6 min and an average contrast volume of 108.9 ± 52.2 mL. During the procedure, one patient experienced retrograde type A aortic dissection that required further intervention. Additionally, one patient required intervention for visceral malperfusion in the same setting. No peri-operative mortality was observed, although 4 patients experienced peri-operative neurologic deficits. The average length of intensive care unit (ICU) stay is 3.9 ± 2.9 days. No peri-operative all-cause mortality was observed. No patients experienced myocardial infarction or spinal cord ischemia. The incidence of short-term outcomes is summarized in Supplementary Table 2.

Long-term outcomes

The average follow-up was 40.7 ± 30.77 months, with up to 8.7 years maximum follow-up. The follow-up was performed with CT scan at 48h post-op, 1 month, 6 months and at 12 months and yearly after unless endoleak occurs. Aortic remodeling with complete thrombosis of the false lumen or resolution of the aortic dissection was observed in 23.3% and 40% of the cases. However, an increase in the average maximum thoracic diameter was observed compared to preoperative values. The average maximum thoracic and abdominal aortic diameters during follow-up were 40.2 ± 30.7 mm and 40.2 ± 15.7 mm, respectively. Over time an endoleak was observed in 10 out of 31 cases with long-term CT data (i.e., type Ia: 12.9%, type Ib: 6.5%, type II: 6.55%, type III: 6.55%) and required thoracic aortic reintervention (Figure 1). The 5-year KM estimate for freedom from any endoleak was 58.9%, and the corresponding survival curve is presented in Figure 2. The overall all-cause mortality rate was 21.9% without any events associated with aortic rupture. Outcomes during follow-up are summarized in Table 3. The 5-year KM curve for freedom from all-cause mortality is illustrated in Figure 3. The 5-year Kaplan – Meier estimates for primary outcomes are summarized in Supplementary Table 3.

Discussion

Aortic dissection is estimated to affect about 4 to 5 persons per 100,000 annually, constituting one of the most common aortic emergency pathologies associated with high morbidity and mortality rates5. Its incidence is increasing as a result of the aging of the population and superior imaging techniques that facilitate early diagnosis. Stanford TBAD originate just distal to the ostium of the left subclavian artery and can extend to the iliac arteries. Type B aortic dissections can be complicated (i.e., rupture, malperfusion) or uncomplicated (e.g., asymptomatic, hypertension, etc.) based on the symptoms at presentation.

Early intervention with an open repair or, more recently, with TEVAR, the first-line therapeutic option, is recommended for complicated aortic dissections5,6, while best medical management is usually preferred for uncomplicated cases7,8. Nonetheless, a significant proportion of uncomplicated cases of TBAD will eventually experience adverse aortic remodeling requiring TEVAR8. Furthermore, experts suggest that “prophylactic” TEVAR in certain occasions of high-risk features may be beneficial9,10. However, long-term data have been limited for studies investigating the outcomes of TEVAR for complicated but uncomplicated aortic dissections, with a reported mean follow-up of fewer than 20 months in most cases11-14. The current study aimed to summarize institutional VQI TEVAR data with long-term follow-up15.

In our study, no peri-operative mortality (within 30 days) was observed, although neurologic deficits were observed in 4 out of 33 patients, with 1 out of 4 cases causing significant disability. Interestingly no incidents of spinal cord ischemia were observed. Although the incidence of neurologic complications is closely correlated with the population characteristics (e.g., trauma vs. no trauma cases, zone 2 vs. zone 3 coverage, etc.), it has been shown that stroke and transient ischemic attack rates can approximate 8% and 3% respectively14-16, with in-hospital mortality reaching up to 4% 6, with patients presenting with visceral ischemia having worse short- and long-term outcomes17,18. This was shown in our study as well. One patient who developed visceral ischemia perioperatively expired 11 weeks after the procedure, accounting for our study’s only short-term all-cause death event.

Aortic-related complications during the chronic stage are common and depending on the severity of the disease at presentation, it can affect up to one-third of the cases9. Similarly, in our study, during an average follow-up of about 41 months, a thoracic reintervention was required in 32.3% of the cases, with endoleaks constituting the most common aortic-related complication (32.4%). A late endoleak is defined as one occurring 30 days post-TEVAR, and the most commonly occurring types of late endoleaks are I and II.19 The reported rates of type I and type II endoleaks after TEVAR range from approximately 0% to 15% and 10-40% in various studies and systematic reviews, depending not only on aortic characteristics (e.g., diameter, aneurysmal degeneration, oversizing) but also on the duration of follow-up. In our study, type Ia, Ib, and II endoleaks were seen in 12.9%, 6.5%, and 6.5% of the cases, respectively. Although there are currently no standardized ways to predict the probability of late aortic expansion and associated aortic-related complications in general, advancements in stent graft technology, operator expertise, and ongoing research are continually improving the outcomes of TEVAR.

While there is current enthusiasm about TEVAR procedures given promising short- and mid-term outcomes, the long-term (e.g., > 2 years) durability of aortic remodeling after TEVAR is an ongoing area of research. In our study, the average maximum thoracic and abdominal aortic diameters were 37.9 mm and 29.9 mm at presentation and 40.2 mm and 40.2 mm during follow-up, respectively. In our cohort, gradually over time, all patients experienced a degree of aortic “degeneration” reflected by larger mean diameters, although only one-third of the patients required a reintervention. Further research is needed to help identify at-risk patients who would benefit from more intense follow-up or a different initial approach. Clinical decision-making is challenged even further by developing newer devices (e.g., branched devices, conformable covered stent grafts, etc.) and techniques (e.g., Petticoat technique); additional research is warranted.

Limitations

The present study has several limitations. It is based on data from a single center, and the study population is small. Using a retrospective cohort design introduces the possibility of unaccounted confounding factors. It has led to a heterogeneous study population, including cases of acute, subacute, and chronic presentations of TBAD, which grossly translated to hyperacute, acute, and subacute interventions. Imaging interpretation was performed by the same reviewers, which reduces variability but may introduce observer bias, as no independent core lab was used.

CONCLUSION

TEVAR is an effective treatment for TBAD, with favorable perioperative outcomes but substantial rates of late endoleaks and reinterventions. Careful patient selection and an individualized approach to optimizing outcomes are crucial for durable outcomes. Future research in stent designs and techniques (e.g., patient-specific, branched/fenestrated, hybrid approaches, etc.), imaging and navigation modalities, and surveillance protocols is warranted to improve patients’ outcomes.

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